1. Field of the Invention
The present invention relates to signal and image processing systems; more particularly, the present invention relates to the real-time spatial and temporal processing of time dependent array data. The present invention also relates to compact, low powered analog VLSI devices that are used in performing spatial and temporal data processing of signals and images.
2. Prior Art
Spatial and temporal filtering is essential to a variety of signal and image processing applications. Applications such as security and surveillance rely on the real-time spatial and temporal processing of live image data. In military applications, spatial and temporal processing is used for the detection and tracking of targets. Image processing systems are important and, in some cases, critical, in applications where limited space, mass, and power requirements are present together with the need for very large computational rates. This is particularly important in military systems on small remote platforms where the computation of spatial frequency filtering involves large convolution operations. Such requirements also exist in commercial systems, particularly in image processing applications, where computational bottlenecks exist such as the interface between focal plane arrays and subsequent image processing. There is an ongoing need for high performance discrimination systems that center on non-stationary spatial and temporal effects as occur for example in missile defense interceptor seeker applications and in commercial bio-mimetic recognition systems.
Spatial frequency filtering in the analog domain by the use of discrete FET circuits forming a resistive array grid is known in the art [1]. This approach is limited to relatively large unit cell areas and although the FET operation in subthreshold conditions resulted in reduced power consumption as compared to conventional designs, the net power dissipation for a large staring array is prohibitive. The signal injection into the resistive grid array is provided by means of controllable conductive inputs. Furthermore, this approach suffers from slow response time that is incompatible with the readout requirements of contemporary high frame rate staring array readout focal plane technology.
An alternative version of the resistive grid has been implemented using a high resistance polymer sheet resistivity approach to form the array lateral interconnections as disclosed in U.S. Pat. No. 6,208,006, issued Mar. 27, 2001, entitled “Thin film spatial filters”, by McElvain et al. This approach allows the extension of resistive array processing to large focal plane formats with low power requirements. Moreover, the method implements a means of processing that both “read-out” a filtered array, and “read-in” a new array image from a multiplexer arrangement thereby allowing an architectural approach to low, high and band pass filtering. Implementation of this approach, although not patented but reported in the literature [2], differs in the method of inserting signals into the resistive grid array when compared to the direct conductance approach. This has been accomplished by the use of capacitor storage to inject charge discretely into the resistive grid array resulting in a Gaussian blurring. However the complexities and control of post foundry processing of the polymer resistive layer makes that process unstable and disadvantageous for production application. The polymer approach has the potential for anisotropic filtering to localize two-dimensional spatial frequency filtering. However, in practice this approach requires a separate anisotropic application for each anisotropic filtering direction and degree of anisotropy. This results in a large number of chips to accomplish the same filtering operation as well as the insertion loss associated with each additional chip.
An alternative approach to resistive grid formation utilizes a switched capacitor resistive grid whereby the filter blurring is created by clocking charge through the lattice of switched capacitor circuits [3]. This approach utilizes the injection of signals to the resistive grid by controllable conductances and allows only isotropic filtering in the switched capacitor resistive grid.
An approach to temporal filtering has been implemented by the use of switched capacitor integration of charge for both high and low pass temporal filtering as disclosed in U.S. Pat. No. 6,040,568, issued Mar. 21, 2000, entitled “Multipurpose readout integrated circuit with in cell adaptive non-uniformity correction and enhanced dynamic range”, by Caulfield et al. In this invention, the device is confined to the application of filtering an image formed by transduction within the device for purposes of sub-frame averaging and scene non-uniformity correction.
The majority of signal and image processing systems in operation today rely on digital processors. Although these systems are extremely versatile, they are not able to process large images at high rates because the digital processors employed in these systems have limited computational power and require a large amount of electrical power to operate (a typical desktop computer consumes about 75 watts). When limited to using only low powered devices, the existing data processing systems cannot handle high data rates. In other words, existing digital processing systems lack the ability to process large amounts of data in real time with limited power.
Analog signal and image processing systems such as disclosed in U.S. Pat. No. 6,208,006, issued Mar. 27, 2001, entitled “Thin film spatial filters”, by McElvain et al. [1][4][5], have recently been implemented and are indeed capable of processing large amounts of data in real-time with low power requirements. Currently available analog signal and image processing systems have little flexibility or programmability, and therefore device operation is highly restrictive with a limited range of applications. It can be appreciated that it would be highly desirable to have a flexible and low-powered apparatus for spatio-temporal filtering. The prior art discussed above does not adequately address these needs.